1. Field of Invention
The present invention relates to an inertial measurement unit (IMU) and, more particularly, to a small size, low weight, minimum power and low cost inertial measurement unit utilizing a plurality of sensors rotated about a single axis.
2. Description of the Prior Art
Existing strap down inertial measurement units typically consist of a cluster of separate gyros and accelerometers of complex electromechanical and/or electro-optical design. These IMUs were originally designed to meet the high performance requirements of an aircraft navigation system with operation times measured in hours. Application of these gyros and accelerometers to flight control IMU's for short duration flight, such as required for expendable weapons which operate in times measured in minutes, has resulted in systems with excessive size, weight, power, and cost, and with inadequate environmental capabilities. Remember that the existing strap down IMUs typically require a separate gyro and accelerometer for each axis within a three axis orthogonal system.
Some systems have been proposed which reduce the number of gyros and accelerometers by using one specialized sensor for sensing two axes. Typically, the specialized sensor is placed upon a spinning shaft. As the multiple sensor is capable of sensing two of the three axes within an orthogonal system, there still remains the requirement for two sets of the sensors as well as the need for motors and bearings to accommodate the spinning axes. This also results in a redundant axis which adds size, weight, and cost.
Another approach to an inertial measurement unit for measuring the specific force and angular velocity of a moving body utilizes an orthogonal triad of rotating accelerometers. This system reduces the number of components required to provide an IMU, but there still remains the requirement for spinning three accelerometers around the three orthogonal axes with the accompanying requirement for bearings and spin motors and resolvers. It has also been suggested that the spinning accelerometers may be vibrated in an oscillating manner instead of spinning around the orthogonal axes.
A further improvement on the arrangement just described vibrates two accelerometers in a back-and-forth arrangement utilizing a parallelogram structure to mount the accelerometers. This arrangement introduces errors in that the motion induced by the parallelogram is not a linear nor a revolving motion but a generally curved motion. The parallelogram structure is also complicated and bulky.